In manufacturing semiconductor devices, in response to a recent request for high densification and high integration, circuitry tends to have a multi-layered wiring structure. For this reason, a burying technique for an electrical connection of a contact hole which connects an Si substrate as the lower layer and a wiring layer as the upper layer becomes important.
In order to make an ohmic contact between a metal wire (plug) such as a W film used to bury such a contact hole or a via hole and an Si substrate as the lower layer, a Ti film is formed on an inner side of the contact hole or a via hole prior to the burying process.
Although such a Ti film has been formed by physical vapor deposition (PVD) in the past, at request of miniaturization and high integration of devices, a chemical vapor deposition (CVD) method having better step coverage is frequently used.
In forming a Ti film using the CVD method, one technology is proposed, in which a TiCl4 gas, an H2 gas and an Ar gas used as film forming gases are introduced into a chamber through a shower head, while a semiconductor wafer is heated by a stage heater, high frequency power is applied to parallel flat plate electrodes to convert these gases into plasma, and the Ti film is formed by the plasma CVD method which causes the reaction between the TiCl4 gas and the H2 gas.
When a TiCl4 gas is used to form a Ti film, a Cl gas produced by the decomposition of the TiCl4 gas remains in the film, which is a factor for increasing the resistance of the Ti film. However, recently, since semiconductor devices are miniaturized and, accordingly, an spatial occupation ratio of the Ti film or other films to the buried metal in a contact hole or a via hole is increased, a Ti film having less remaining Cl and thus having low resistance is needed.
In order to reduce the resistance of a Ti film by decreasing the amount of Cl remaining therein, increasing the film forming temperature to 600 degrees C. or so for the desorption of Cl may be considered. However, due to a recent trend in which a material having a low heat resistance temperature is used in devices or from a viewpoint of prevention of impurity diffusion, the film formation at low temperature not greater than 450 degrees C. is pursued. Thus, it is impractical to form a film at high temperature.